Sodium bicarbonate has become a substantial component of hemo and peritoneal dialysate solutions. In many situations, these dialysate solutions are prepared and transported in ready to use form to the site of use, most typically a dialysis clinic. This has the drawback that large volumes of water need to be transported, thereby increasing the cost of transportation significantly as well as requiring large areas for storage of sufficient solution for use. In an effort to reduce the large volumes of water contributing to cost and space and sterility issues, dry powder forms of the dialysis components or dry mixtures of the needed components have been tried. The difficulty here is that the components must be diluted, typically batch style, which increase preparation time at the clinic site and require large volume mixing tanks for each dialysis unit, thereby restricting the available floor space for dialysis units themselves and thereby limiting the number of dialysis patients that can be treated in a given dialysis clinic to less than would otherwise be needed. As such, efforts have been underway to utilize in line cartridges of the dialysis components for dissolution to the appropriate concentrations with locally supplied reverse osmosis water. Such units have typically used cartridges which contained dry powder. Where dry powders have been used, the problems associated therewith include those such as inconsistent concentrations flowing out of the cartridge, which require concentration monitoring and adjustment of various other dilution controls to result in the appropriate concentrations in the final dialysate.
In addressing the above concerns, the instant inventor and other coworkers have proposed a micronized slurry of sodium bicarbonate for use in such cartridges. The micronized slurry eliminates the large water tank and transportation issues of the solutions, and overcomes the dissolution inconsistency of the dry powder cartridges. Such slurries are set forth in detail in copending application Ser. No. 09/814,401, filed Mar. 22, 2001, entitled MICRON SIZED BICARBONATE PARTICLES AND SLURRYS CONTAINING THE SAME, the full text of which is incorporated herein by reference.
In preparing the full dialysate solution, there are generally two pre-solutions prepared which are mixed just prior to exposing the patient or patient's blood to the full dialysate. One of these pre-solutions contains sodium bicarbonate and sodium chloride in a weight ratio of sodium bicarbonate to sodium chloride of about 3:1. When dry powder bulk material (for bulk dilution before beginning the dialysis treatment) the sodium bicarbonate and sodium chloride have been typically been pre-blended in the appropriate ratio and the clinic staff assure completed dissolution of the materials before they are used.
The saturation solubility of sodium bicarbonate in water is generally known to decrease with temperature. For example, sodium bicarbonate saturation concentrations in water are about 10% weight/volume at 25° C., 8.5% at 22° C., and about 7% at 10° C. The saturation solubility of sodium chloride in water is about 36.1% weight/volume at 25° C., 35.7% at 22° C., and about 35.7% at 10° C. Owing to the solubility differences between these two components, especially in the greater solubility of sodium chloride, one would not have expected that one could combine both sodium chloride and sodium bicarbonate in a single slurry and achieve consistent effluent concentration upon dissolution of the slurry over the effective lifetime of the slurry dissolution time where the sodium bicarbonate concentration would exceed the sodium chloride concentration.